The present invention relates in general to ionization detectors, and more particularly, to an ionization detector of the multiple chamber type preferably employing only a single ionization source associated with each chamber of the detector.
Ionization detectors have recently found quite widespread usage especially in the residential area, brought about primarily by a decrease in cost of constructing these detectors. However, there is still a need for further improvement in performance without however, creating an attendant increase in the manufacturing cost of the detector. It is one purpose of the present invention to provide such improvement in performance without an increase in manufacturing cost.
There currently exists three basic types of ionization detectors including a single source/single chamber detector, a single source/dual chamber detector, and a dual source/dual chamber detector. The single source ionization detector is used with a single chamber having an outboard series resistor. When a single source is used with a dual chamber the radiation from the single source emanates through both chambers with there usually being provided a grid or opening separating the chambers to permit the radiation to emanate into both chambers. The most common construction is the dual source/dual chamber detector. This construction can also include a single source coated with radioactive material on both sides and placed between the chambers. Again, an opening may exist between the two chambers. Also included in this type is a dual chamber housing having a source disposed in each chamber.
In a dual chamber construction employing a single source, the ionization is strictly dependent upon the geometry of the chambers and the relative position of the orifice between chambers that permits ions to penetrate into the second chamber. The specific activity of radioactive sources may vary and thus means are usually provided for compensation for this variation. It is typical to achieve this adjustment by adjusting the position of the source closer to or further away from the center electrode or, alternatively, by moving electrodes relative to each other. In this instance, if a source is connected to an electrode, then the electrode and source are moved in unison. With the dual chamber construction and the use of only a single source, generally the opening between chambers has to be quite large, however, this results in reduced sensitivity especially for slow smoldering fires due to the likelihood of combustion particles reaching the reference chamber.
When two sources are used in a dual chamber construction, one source is associated with each chamber. Tolerances of each source may lead to an imbalance between the ionization in each chamber. In the dual chamber construction similar adjustment means may be used as previously discussed with regard to the single ionization source arrangement. Additionally, an ion-capturing means may be employed such as the one shown in U.S. Pat. No. 4,021,671. Also, in the two-source embodiment, this requires two sources and two supports for the source thus complicating the construction and making for a more costly detector.
Accordingly, it is one object of the present invention to provide an approved dual chamber ionization detector, one in which only a single source is employed being associated with both chambers of the detector.
Another object of the present invention is to provide a multiple chamber ionization detector having infinite and readily simple adjustment of the ionization in each chamber of the detector.
A further object of the present invention is to provide a multiple chamber ionization detector that does not require very precise tolerances of mechanical parts and the very precise tolerances of the radioactive source itself.
Still another object of the present invention is to provide an ionization detector that is of relatively simple construction and that is relatively uncomplex and that is capable of manufacture at a relatively inexpensive manufacturing cost.
Still another object of the present invention is to provide a detector that uses only one ionization source and yet does not sacrifice performance with the use of only one source. With this detector the long term decay of the source is automatically compensated for because of the use of only one source and the ratio of ionization is maintained constant in each chamber even after this long term decay of the output of the source.
Still a further object of the present invention is to provide an ionization detector that is readily adapted for use with almost any type of approved radiation source including, for example, a beta ionization source.